see http://homer.ncm.com/linux-multicast/
There are implementations of mrouted, ivs, nv, vic, vat, sd (sdr ist not available) and wb available for Linux (ftp.funet.fi); for wb no special hardware is needed, vat uses the standard Linux sound support, vic works only in receiving mode, no video frame grabber support is included; nv and ivs support the Screen Machine II as frame grabber.
nt is a tools for shared document, but you can use emacs for that as well...